JP7258607B2 - Active materials, electrodes, secondary batteries, battery packs and vehicles - Google Patents

Description

TECHNICAL FIELD Embodiments of the present invention relate to active materials, electrodes, secondary batteries, battery packs, and vehicles.

Non-aqueous electrolyte batteries using a negative electrode made of a graphite material or a carbonaceous material that absorbs and releases lithium ions have been commercialized as high-energy-density batteries for portable devices. In recent years, LiNi _a Co _{b Al 1-ab O 2 and LiNi a Co b Mn 1-ab} O ₂ and LiNi _a Co _b Mn _1-ab O have been used as cathode active materials in place of LiCoO ₂ and LiMn ₂ O ₄ in order to further improve the energy density of batteries. ₂ and other Ni-containing lithium metal oxides are being put to practical use.

On the other hand, when it is installed in vehicles such as automobiles and trains, it must be chemically and electrochemically stable for the constituent materials of the positive electrode and negative electrode because of storage performance in high-temperature environments, cycle performance, and long-term reliability of high output. Materials with excellent properties, strength, and corrosion resistance are required. Furthermore, materials for the positive and negative electrodes are required to have high performance in cold climates, high output performance in a low temperature environment (−40° C.), and long life performance. On the other hand, as a non-aqueous electrolyte, development of non-volatile and non-flammable electrolyte solutions is progressing from the viewpoint of improving safety performance, but it has not been put into practical use yet due to deterioration of output characteristics, low temperature performance and long life performance.

As explained above, high-temperature durability, cycle life, safety, and output performance are issues to be addressed in order to install lithium-ion batteries in vehicles.

By using a titanium oxide such as TiO ₂ or Li ₄ Ti ₅ O ₁₂ as the negative electrode instead of a graphite material or a carbonaceous material, the life performance and safety of the battery are improved, but the energy density is low. descend. The decrease in the energy density of the battery is due to the fact that the negative electrode potential (vs. Li) of the titanium oxide is as high as about 1.5 V, the battery voltage is lowered, and the negative electrode capacity is small. Therefore, in order to increase the battery capacity, a titanium-based oxide having a high capacity and excellent output performance and life performance is required.

JP 2010-287496 A US2012/0052401A1 US publication

An object of the embodiments is to provide an electrode and a secondary battery that are excellent in large current performance and cycle life performance, an active material capable of realizing these, a battery pack and a vehicle that include the secondary battery.

According to an embodiment, an active material comprising monoclinic niobium-titanium composite oxide particles capable of intercalating and deintercalating Li ions, and carbon fibers covering at least part of the surfaces of the niobium-titanium composite oxide particles. is provided. The monoclinic niobium-titanium composite oxide particles satisfy the following formula (1). The average primary particle size of the monoclinic niobium-titanium composite oxide particles is in the range of 0.05 μm or more and 2 μm or less. Carbon fibers contain one or more metal elements selected from the group consisting of Fe, Co and Ni. The carbon fiber satisfies the following formula (2). Also, the average fiber diameter of the carbon fibers is in the range of 5 nm or more and 100 nm or less.

1.5≦(α/β)≦2.5 (1)
1/10000≤(γ/σ)≤1/100 (2)
where α is the number of moles of Nb in the monoclinic niobium-titanium composite oxide particles, β is the number of moles of Ti in the monoclinic niobium-titanium composite oxide particles, and γ is the number of moles of all metal elements in the carbon fiber. In weight, σ is the carbon weight of the carbon fiber.

Further, according to embodiments, there is provided an electrode including an active material according to embodiments.

Furthermore, according to the embodiment, there is provided a secondary battery including a positive electrode, a negative electrode containing the active material according to the embodiment, and a non-aqueous electrolyte.

Furthermore, according to the embodiment, a battery pack including the secondary battery according to the embodiment is provided.

Moreover, according to the embodiment, a vehicle including the battery pack according to the embodiment is provided.

FIG. 2 is a partially cutaway cross-sectional view of the secondary battery of the embodiment; FIG. 2 is a side view of the battery of FIG. 1; FIG. 2 is a cross-sectional view of the secondary battery of the embodiment cut in a direction perpendicular to the extending direction of the terminals; FIG. 4 is an enlarged cross-sectional view of part A in FIG. 3 ; The perspective view which shows an example of the assembled battery containing the secondary battery of embodiment. 1 is an exploded perspective view of a battery pack according to an embodiment; FIG. FIG. 7 is a block diagram showing an electric circuit of the battery pack of FIG. 6; 1 is a schematic diagram showing an example of a vehicle equipped with a secondary battery according to an embodiment; FIG. The figure which showed roughly the other example of the vehicle which concerns on embodiment. FIG. 2 shows a scanning electron micrograph of the active material of Example 1; FIG. 2 shows a scanning electron micrograph of the active material of Example 1;

[First Embodiment]
According to the embodiment, monoclinic niobium-titanium composite oxide particles capable of occluding and releasing Li ions, and carbon fibers covering at least part of the surface of the monoclinic niobium-titanium composite oxide particles. Provided is an active material comprising: The monoclinic niobium-titanium composite oxide particles satisfy the following formula (1). The monoclinic niobium-titanium composite oxide particles have an average primary particle size of 0.05 μm or more and 2 μm or less. The carbon fiber contains one or more metal elements selected from the group consisting of Fe, Co and Ni, and satisfies the following formula (2). The average fiber diameter of carbon fibers is in the range of 5 nm or more and 100 nm or less.

1.5≦(α/β)≦2.5 (1)
1/10000≤(γ/σ)≤1/100 (2)
where α is the number of moles of Nb in the niobium-titanium composite oxide particles, β is the number of moles of Ti in the niobium-titanium composite oxide particles, γ is the weight of all metal elements in the carbon fiber, and σ is the weight of carbon in the carbon fiber. is.

Since the carbon fibers easily disperse on the surfaces of the niobium-titanium composite oxide particles, the carbon fibers are uniformly dispersed on the surfaces of the niobium-titanium composite oxide particles to coat the surfaces. As a result, the electrode resistance is lowered. In addition, the niobium-titanium composite oxide undergoes a large volume change when the lithium storage capacity is increased in order to increase the charge capacity. The active material of the embodiment can maintain the effect of the electron conduction network due to the carbon fiber coating even when the volume expansion and contraction due to the absorption and desorption of lithium ions is repeated. As a result, the rate performance and cycle life performance of the battery are significantly improved.

The metal elements in ^the carbon fiber are eluted into the electrolyte when exposed to a high potential. Since it does not deposit on the separator, there is no risk of inducing an internal short circuit.

The niobium-titanium composite oxide particles are Li _x TiM _w Nb _2±y O _7±z (0≦x≦5, 0≦y≦0.5, −0.3≦z≦0.3, 0≦w≦0 .01, and M is at least one kind of metal other than Ti and Nb). The niobium-titanium composite oxide particles are mixed with carbon fibers to facilitate uniform dispersion and surface coating, resulting in a uniform electron conduction network in the electrode and a significant improvement in rate performance and cycle life performance.

Also, M preferably contains at least one metal element selected from the group consisting of K and Ta. Since metal elements such as K and Ta function as fluxes, it is possible to synthesize a niobium-titanium composite oxide by low-temperature heat treatment. As a result, it becomes easier to obtain granular particles. If the heat treatment temperature during synthesis is high, crystal growth is promoted and the particle shape becomes rod-like. Rod-shaped particles tend to crack due to expansion and contraction associated with charge-discharge cycles. As a result, the electronic conduction network may be interrupted in the electrode and the cycle life may be reduced. By setting the amount in the appropriate range of 0≦w≦0.01, the niobium-titanium composite oxide particles can be made into a granular shape, and the electron conduction network can be maintained by the surface coating with carbon fibers. Cycle life performance and discharge rate performance can be significantly improved.

w preferably satisfies the formula (3): 0.001≤w≤0.005. As a result, side reactions caused by the element M can be suppressed, and collapse of the electronic conduction network due to cracking of particles accompanying the absorption and release of lithium ions can be suppressed.

The value of (γ/σ) in formula (2) preferably satisfies formula (4): 1.5/10000≦(γ/σ)≦1/1000. This improves the electron conduction network between the active material particles, thereby improving the cycle life performance and the discharge rate performance.

By satisfying the formulas (3) and (4), the electron conduction network between the active material particles is further improved, so that the effect of improving the cycle life performance and the discharge rate performance is increased.

The active material will be described in detail below.

The monoclinic niobium-titanium composite oxide particles satisfy the formula (1): 1.5≦(α/β)≦2.5. Here, α is the number of moles of Nb in the niobium-titanium composite oxide particles, and β is the number of moles of Ti in the niobium-titanium composite oxide particles. A larger (α/β) can improve the capacity of the active material, but reduces the electronic conductivity of the niobium-titanium composite oxide. In order to obtain good electronic conductivity and high capacity, it is desirable that the value of (α/β) is within the range of formula (1). (α/β) is preferably 0.8≦(α/β)≦1.9. Within this range, a niobium-titanium composite oxide containing monoclinic Li _x TiNb ₂ O ₇ and Na _x TiNb ₂ O ₇ as well as a titanium oxide phase (e.g., rutile TiO ₂ , TiO, etc.) is obtained. , The electron conductivity of the composite oxide is improved, and the large current discharge performance is excellent.

The monoclinic niobium-titanium composite oxide particles may be primary particles or secondary particles obtained by agglomeration of primary particles. Primary particles are preferred. This is because the carbon fibers are more uniformly dispersed in the niobium-titanium composite oxide particles.

The average primary particle size of the monoclinic niobium-titanium composite oxide particles is preferably in the range of 0.05 μm or more and 2 μm or less. This particle size reduces the resistance associated with the diffusion of Li ions and Na ions in the particles, greatly improving the large current discharge performance and the rapid charge performance. By setting the average primary particle size to 0.05 μm or more, high crystallinity can be obtained, and thus high capacity can be obtained. A more preferable lower limit of the average primary particle size is 0.1 μm. More preferably, the average primary particle size of the niobium-titanium composite oxide particles is 0.5 μm or less. In addition, the primary particle size may be the diameter of a particle.

The average primary particle size of the niobium-titanium composite oxide particles is measured, for example, by the following method. Using a laser diffraction distribution measuring device (Shimadzu Corporation laser diffraction particle size distribution measuring device SALD-300), first, about 0.1 g of a sample, a surfactant, and 1 to 2 mL of distilled water are added to a beaker. After sufficiently stirring, the mixture is poured into a stirring water tank, the light intensity distribution is measured 64 times at intervals of 2 seconds, and the particle size distribution data is analyzed. The average primary particle size is measured after separating the carbon fibers from the niobium-titanium composite oxide particles. The separation method will be described later.

The monoclinic niobium-titanium composite oxide is Li _x TiM _w Nb _{2±yO 7±z} (0≦x≦5, 0≦y≦0.5, −0.3≦z≦0.3, 0 ≦w≦0.01, and M is at least one kind of metal other than Ti and Nb).

The Li amount x of the monoclinic niobium-titanium composite oxide may vary depending on the intercalation and deintercalation of lithium ions during charging and discharging. Moreover, the monoclinic niobium-titanium composite oxide does not have to contain lithium at the time of synthesis. Further, a monoclinic niobium-titanium composite oxide that does not contain lithium at the time of synthesis can store lithium through intercalation and deintercalation of lithium ions during charging and discharging.

Examples of M include at least one metal element selected from the group consisting of K and Ta. Since metal elements such as K and Ta function as fluxes, it is possible to synthesize a niobium-titanium composite oxide by low-temperature heat treatment. As a result, it becomes easier to obtain granular particles. By setting the amount in the appropriate range of 0≦w≦0.01, the niobium-titanium composite oxide particles can be made into a granular shape, and the electron conduction network can be maintained by the surface coating with carbon fibers. Cycle life performance and discharge rate performance can be significantly improved. w preferably satisfies the formula (3): 0.001≤w≤0.005. As a result, side reactions caused by the element M can be suppressed, and collapse of the electronic conduction network due to cracking of particles accompanying the absorption and release of lithium ions can be suppressed.

y ranges from 0 to 0.5. If this range is exceeded, the electrode capacity may decrease due to phase separation exceeding the solid solubility limit. A more preferable range is 0.05≤y≤0.2.

z varies depending on the reduction state of the monoclinic niobium-titanium composite oxide. If z exceeds −0.3, niobium is reduced in advance, resulting in deterioration of electrode performance and possible phase separation. On the other hand, z=+0.3 is within the range of measurement error.

The monoclinic niobium-titanium composite oxide may contain at least one selected from the group consisting of Mg, Al, V, Fe, Mo, Sn and W.

The carbon fiber contains one or more metal elements selected from the group consisting of Fe, Co and Ni, and satisfies the following formula (2).

1/10000≤(γ/σ)≤1/100 (2)
γ is the weight of all metal elements in the carbon fiber, and σ is the carbon weight of the carbon fiber.

Examples of carbon fibers containing the metal element include vapor-grown carbon fibers containing the metal element as a catalyst. Examples of vapor-grown carbon fibers include multi-walled carbon nanotubes and single-walled carbon nanotubes. Among the above metal elements, Fe, Co, or both of Fe and Co are preferable.

When the value of (γ/σ) is less than 1/10000, it becomes difficult to uniformly disperse the carbon fibers on the niobium-titanium composite oxide particles to coat the surface thereof, resulting in deterioration of cycle life performance. On the other hand, when the value of (γ/σ) exceeds 1/100, the ratio of the fiber length to the fiber diameter (fiber length/fiber diameter) exceeds the appropriate range, so the carbon fibers are dispersed in the electrode. It becomes difficult to coat the surface of the niobium-titanium composite oxide particles, and the cycle life performance deteriorates. More preferably, the value of (γ/σ) satisfies the formula (4): 1.5/10000≦(γ/σ)≦1/1000. The content of the metal element can be adjusted by acid treatment or the like.

Further, by satisfying the formulas (3) and (4), the electron conduction network between the active material particles is further improved, so that the effect of improving the cycle life performance and the discharge rate performance is increased.

The average fiber diameter of carbon fibers is in the range of 5 nm or more and 100 nm or less. If the average fiber diameter is less than 5 nm or more than 100 nm, it becomes difficult to uniformly disperse the carbon fibers in the niobium-titanium composite oxide particles to coat the surfaces of the niobium-titanium composite oxide particles. A more preferable range of the average fiber diameter is 10 nm or more and 90 nm or less.

The addition ratio of carbon fibers (ratio of carbon fiber weight to weight of niobium-titanium composite oxide particles, carbon fiber/niobium-titanium composite oxide) is preferably in the range of 0.1% by weight or more and 5% by weight or less. Within this range, the electron conduction network can be made uniform and a high electrode density can be maintained, and the electrode resistance can be reduced and the electrode volumetric capacity can be increased. A more preferable range is 0.2% by weight or more and 3% by weight or less.

The ratio of the fiber length to the fiber diameter of the carbon fibers (fiber length/fiber diameter) is preferably 10 or more and 1000 or less. Within this range, the electron conduction network can be made uniform and a high electrode density can be maintained, and the electrode resistance can be reduced and the electrode volumetric capacity can be increased. A more preferable range is 100 or more and 800 or less.

The active material of the embodiment can be produced, for example, by the following method. First, the starting materials are mixed. An oxide or salt containing Li, Ti, and Nb is used as a starting material for the niobium-titanium composite oxide. Also, the salt used as the starting material for the other additive elements of the niobium-titanium composite oxide should be a salt such as a hydroxide salt, a carbonate, or a nitrate that decomposes at a relatively low melting point to form an oxide. is preferred. In order to reduce the primary particle size, it is preferable to use a powder having an average particle size of 2 μm or less, preferably 0.5 μm or less, as the starting material.

The starting materials are mixed at a molar ratio (α/β) of 1.5≦(α/β)≦2.5. Further, the other additive element M (at least one kind of metal other than Ti and Nb, preferably at least one kind of element selected from the group consisting of K and Ta) is a crystal obtained by substituting a part of Nb with the element M. It is preferred to mix in molar ratios such that the overall charge remains neutral. As a result, TiM _w Nb _{2 ± y} O _{7 ± z} (0 ≤ y ≤ 0.5, 0 ≤ w ≤ 0, 01, -0.3 ≤ z ≤ 0.3, M is at least one other than Ti and Nb) It is possible to obtain an active material containing a monoclinic niobium-titanium composite oxide represented by the type of metal). On the other hand, TiM _w Nb _{2±yO 7±z} can be obtained by adjusting the addition amount even if the addition method does not keep the total charge neutral.

The resulting mixture is then ground to obtain a mixture that is as homogeneous as possible. The resulting mixture is then fired. Firing is carried out in the temperature range of 500 to 1200°C, more preferably in the range of 700 to 1000°C. Existing equipment can be utilized by carrying out the sintering temperature at 1000° C. or less. By this method, a powder containing a monoclinic niobium-titanium composite oxide having an average primary particle size of 2 μm or less represented by TiM _w Nb _2±y O _7±z can be obtained. In addition, a monoclinic niobium-titanium composite oxide powder having an average primary particle size of 1 μm or less can be obtained using a hydrothermal synthesis method. When lithium ions are electrochemically occluded using this niobium-titanium composite oxide as an _electrode , a crystal structure of _{LixTiMwNb2 ±yO7 ±z} (0≤x≤5, preferably 0<x≤5) is obtained. (battery charged state).

In the method of coating the surface of niobium-titanium composite oxide particles with carbon fibers, carbon fiber powder is added to an aqueous solution and mixed with stirring to prepare a dispersion solvent in which the particles are uniformly dispersed at a predetermined concentration. After that, niobium-titanium composite oxide particles are added to the dispersion solvent and stirred and mixed, and then a binder (e.g., cellulose nanofiber, carboxymethyl cellulose, styrene-butadiene rubber, etc.), a conductive agent (e.g., graphite, carbon fiber, acetylene black, etc.). carbon material) is added and mixed by stirring to prepare a slurry. It is preferable to use cellulose nanofibers as the binder because the carbon fibers can be dispersed well, the surface of the niobium titanium oxide particles can be uniformly coated, and the electrode resistance can be reduced.

The slurry is applied to a current collector, dried, and pressed to form an active material-containing layer on the current collector, thereby obtaining an electrode. By observing the active material-containing layer with an electron microscope (e.g., scanning electron microscope, SEM), carbon fibers with an average fiber diameter of 5 nm or more and 100 nm or less adhere to at least a part of the niobium-titanium composite oxide particle surface. It can be confirmed that they are integrated with a binder, metal, or the like. Examples of SEM photographs are shown in Examples.

First, when an electrode containing an active material is included in the secondary battery, the electrode is taken out by the following method. Here, the case where the electrode is the negative electrode will be described as an example. First, the secondary battery is discharged. Specifically, in an environment of 25° C., the secondary battery is discharged to the discharge lower limit voltage at a current value of 0.2 C or less to enter a discharged state. Put the discharged battery in a glove box filled with argon gas. Remove the target electrode (eg, negative electrode) from the battery in the glove box. The removed electrode is washed with ethyl methyl ether solvent. Thus, an electrode sample is obtained.

A quantitative analysis of the amount of metal elements present in the carbon fibers and a method of calculating the average fiber diameter of the carbon fibers using the obtained electrode samples will be described below.

For the electrode sample, the carbon fibers and the niobium-titanium composite oxide particles are separated from the current collector by ultrasonic treatment, and the carbon fibers are extracted using centrifugal separation. The type of solvent used for extraction is changed according to the type of binder contained in the electrode. For example, when carboxymethyl cellulose (CMC) or styrene-butadiene rubber (SBR) is contained as the binder, water is used as the extraction solvent. On the other hand, when polyvinylidene fluoride (PVdF) is contained as the binder, an organic solvent such as n-methylpyrrolidone (NMP) is used as the extraction solvent. This extraction separates the niobium-titanium composite oxide particles and the carbon fibers.
The carbon fibers extracted by the above method are subjected to IPC (ICP-MS: Inductively Coupled Plasma-Mass Spectrometry) to obtain the carbon weight of the carbon fibers and the weight of metal elements in the carbon fibers.

The carbon fibers extracted by the above method are observed with a scanning electron microscope (SEM) at a magnification of 10000 times, and the width (diameter ) is measured. The average of the measured width values is taken as the average fiber diameter to be determined. Measurement is performed on all carbon fibers present within the field of view.

For the niobium-titanium composite oxide particles extracted by the above method, the molar ratio of the elements Ti and Nb is obtained by ICP (Inductively Coupled Plasma) analysis. Specifically, in the ICP analysis, niobium-titanium composite oxide particles as a sample are weighed in a Pt crucible and decomposed by alkali fusion to prepare a measurement solution. Nb and Ti can be quantitatively measured by ICP emission spectrometry using an internal standard method, for example, an ICP emission spectrometer (SPS-4000 of Hitachi High-Tech Science Co., Ltd.).

Further, the average primary particle size of the niobium-titanium composite oxide particles extracted by the above method is measured by the above method.

According to the active material of the first embodiment described above, monoclinic niobium-titanium composite oxide particles that satisfy the formula (1) and have an average primary particle size of 0.05 μm or more and 2 μm or less, Fe, Co, and It contains one or more metal elements selected from the group consisting of Ni, satisfies the formula (2), and contains carbon fibers having an average fiber diameter in the range of 5 nm or more and 100 nm or less, so large current performance and cycle life It is possible to provide an electrode or secondary battery active material with excellent performance.

(Second embodiment)
According to a second embodiment, an electrode is provided. The electrode contains the active material of the first embodiment. The electrode includes a current collector and an active material-containing layer held on at least one main surface of the current collector and containing an active material, a binder, and optionally a conductive agent.

The active material may be only the active material according to the first embodiment, or may contain active materials other than this active material.

Examples of other active materials include metal oxides, metal sulfides, metal fluorides, metal nitrides. Titanium-containing metal oxides are preferred from the viewpoint of improving cycle life performance. Examples of titanium-containing metal oxides include lithium-titanium-containing oxides and titanium-containing oxides. Examples of lithium-titanium-containing oxides include those having a spinel structure (for example, general formula Li _4/3+a Ti _5/3 O ₄ (0≦a≦2)) and those having a ramsdellide structure (for example, general Formula Li2 _{+ aTi3O7} ( _0≤a≤1 ) _, Li1 _{+ bTi2O4} (0≤b≤1), Li1.1 _{+ bTi1.8O4} (0≤b≤1), _{Li 1.07+b} Ti _1.86 O ₄ (0≤b≤1)), Nb, Mo, W, P, V, Sn, Cu, Ni and Fe Lithium titanium containing at least one element selected from the group consisting of Contains complex oxides and the like. Examples of lithium-titanium-containing oxides include Li _{2+a Ad} Ti _6-b B _b O _14-c (A is one or more elements selected from Na, K, Mg, Ca, and Sr; metal element, 0≦a≦5, 0≦b≦6, 0≦c≦0.6, 0≦d≦3). The crystal structure of the lithium-titanium-containing composite oxide may be a crystal structure of space group Cmca.

Titanium-containing oxides can be represented by the general formula Li _a TiO ₂ (0≦a≦2). In this case, the composition formula before charging is TiO ₂ . Examples of titanium oxide include monoclinic structure (bronze structure (B)) titanium oxide, rutile structure titanium oxide, anatase structure titanium oxide, and the like. TiO ₂ (B) having a monoclinic structure (bronze structure (B)) is preferred, and low crystallinity with a heat treatment temperature of 300 to 600° C. is preferred.

The particle shape of the active material is preferably granular, but may also be fibrous.

The electrode porosity (excluding the current collector) is desirably in the range of 20-50%. This makes it possible to obtain a high-density electrode having excellent affinity between the electrode and the non-aqueous electrolyte. A more preferred range of porosity is 25-50%.

Examples of current collectors include nickel foil, copper foil, stainless steel foil, aluminum foil, and aluminum alloy foil. The current collector is desirably aluminum foil or aluminum alloy foil. The purity of the aluminum foil is preferably 99.99% or more. The aluminum alloy is preferably an alloy containing elements such as magnesium, zinc and silicon. On the other hand, the content of transition metals such as iron, copper, nickel and chromium is preferably 100 ppm or less. A mesh shape can also be used for the current collector in addition to the foil shape.

The thickness of the current collector is preferably 20 μm or less, more preferably 15 μm or less.

Examples of conductive agents include acetylene black, carbon black, coke (preferably having an average particle size of 10 μm or less at a heat treatment temperature of 800° C. to 2000° C.), carbon nanotubes, carbon fibers, graphite, TiO, TiC, TiN, and the like. and metal powders such as Al, Ni, Cu, and Fe can be used singly or in combination. By using carbon nanotubes and carbon fibers having a fiber diameter of 1 μm or less, the electrode resistance is reduced and the cycle life performance is improved.

Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, acrylic rubber, styrene-butadiene rubber (SBR), cellulose nanofiber (CeNF), carboxymethyl cellulose (CMC ), core-shell binders, and polyimides. One type or two or more types of binders can be used.

In the active material-containing layer, the compounding ratio of the active material, the conductive agent, and the binder can be in the range of 90 to 99% by weight of the active material, 0 to 8% by weight of the conductive agent, and 2 to 7% by weight of the binder. preferable.

The BET specific surface area by N ₂ adsorption of the active material and electrode is measured under the following conditions, for example. Two electrodes of 1 g of powdered active material or 2×2 cm ² are cut and used as samples. A BET specific surface area measuring device manufactured by Yuasa Ionics Co., Ltd. is used, and nitrogen gas is used as the adsorption gas.

The porosity of the electrode was determined by comparing the volume of the active material-containing layer with the volume of the active material-containing layer when the porosity was 0%, and subtracting the increase from the volume of the active material-containing layer when the porosity was 0%. It is calculated assuming that it is the pore volume. The volume of the active material-containing layer is the sum of the volumes of the active material-containing layers on both sides of the current collector when the active material-containing layers are formed on both sides of the current collector.

Electrodes can be obtained, for example, by the method described in the first embodiment.

According to the electrode of the second embodiment, since it contains the active material of the first embodiment, it is possible to provide an electrode excellent in large current performance and cycle life performance.

(Third embodiment)
A third embodiment provides a secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The electrode of the second embodiment can be used as a positive electrode or a negative electrode. Here, an example in which the electrode is used as the negative electrode will be described. The secondary battery of the third embodiment can have a separator disposed between the positive electrode and the negative electrode, and can further include a container for housing these and the non-aqueous electrolyte.

The positive electrode, non-aqueous electrolyte, separator, and container are described below.

(positive electrode)
The positive electrode is held on at least one main surface of a positive electrode current collector and one or both surfaces of the current collector, and contains a positive electrode active material-containing layer containing an active material, a conductive agent, and a binder. including.

Examples of positive electrode active materials include Ni-containing lithium metal oxides, spinel-structured lithium manganese oxides, lithium cobalt composite oxides, lithium nickel composite oxides, lithium nickel cobalt composite oxides, and lithium cobalt aluminum composite oxides. , lithium nickel aluminum composite oxide, lithium nickel cobalt manganese composite oxide, spinel structure lithium manganese nickel composite oxide, lithium manganese cobalt composite oxide, olivine structure lithium-containing phosphate compound, fluorinated iron sulfate, lithium nickel cobalt Manganese composite oxides and the like are included. In addition, graphite, a carbon material, or activated carbon having a capacitor capacity can be used as the positive electrode. One kind or two or more kinds of positive electrode active materials can be used.

Examples of spinel-structure lithium-manganese composite oxides include Li _x Mn ₂ O ₄ (0<x≦1), Li _x MnO ₂ (0<x≦1), and LiMn _1.5 Ni _0.5 O ₄ .

Lithium-cobalt composite oxides include, for example, Li _x CoO ₂ (0<x≦1).

Examples of lithium-nickel-aluminum composite oxides include Li _x Ni _1-y Al _y O2 (0<x≦1, 0<y≦1).

Lithium-nickel-cobalt composite oxides include, for example, Li _x Ni _1-yz Co _y Mn _z O ₂ (0<x≦1, 0<y≦1, 0≦z≦1, 0<1-y- z<1) and the like.

Lithium-manganese-cobalt composite oxides include, for example, Li _x Mn _y Co _1-y O ₂ (0<x≦1, 0<y<1).

Lithium-manganese-nickel composite oxides having a spinel structure include, for example, Li _x Mn _2-y Ni _y O ₄ (0<x≦1, 0<y<2).

Examples of lithium-containing phosphate compounds having an olivine structure include Li _x FePO ₄ (0<x≦1), Li _x Fe _1-y Mn _y PO ₄ (0<x≦1, 0≦y≦1), Li _xCoPO4 (0 _< x≤1) _{, LixMnPO4} (0 _< x≤1), LiMn1 _{- xyFexMgyPO4} (0≤x≤0.5 _and 0≤y≤0.5) etc.
Examples of fluorinated iron sulfate include Li _x FeSO ₄ F (0<x≦1).

Lithium-nickel-cobalt-manganese composite oxides _{include ,} for example, _{LixNi1 -y- zCoyMnzO2} (0<x≤1.1, 0<y≤0.5, 0<z≤0.5 , 0<1-yz<1) and the like.

Lithium metal oxides containing Ni include, for example, lithium nickel oxides (eg LiNiO ₂ ), lithium nickel cobalt oxides (eg LiNi _a Co _1-a O ₂ ), lithium nickel cobalt aluminum oxides (eg LiNi _a Co _b Al _1-ab O ₂ ), lithium nickel cobalt manganese oxide (eg, LiNi _a Co _b Mn _1-ab O ₄ , where 0<a<1, 0<b<1, 0<( 1-ab)<1) and the like. Here, when the Ni-containing lithium metal oxide is represented by the general formula LiNi _x M _1-x O ₂ (M is at least one kind of metal other than Ni), x ranges from 0.5 to 1. preferable. An oxide that satisfies this range has a high capacity and a high energy density. Therefore, when combined with the active material according to the embodiment, high-temperature cycle life performance, high output performance, and safety performance can be significantly improved.

More preferable positive electrode materials are LiFePO ₄ and Li _x Fe _1-y Mn _y PO ₄ in terms of cycle life performance. LiNi _x M _1-x O ₂ (M is at least one kind of metal other than Ni, and 0.5≦x≦1) is preferable in terms of battery capacity.

At least one element selected from the group consisting of Mg, Al, Ti, Nb, Sn, Zr, Ba, B and C (hereinafter referred to as first element ) may be present. Such a positive electrode active material can suppress an oxidative decomposition reaction of a non-aqueous electrolyte in a high-temperature environment, and thus can suppress an increase in resistance. Thereby, the high-temperature cycle life performance of the secondary battery can be greatly improved.
The first element is attached in the form of metal oxide particles and/or phosphor oxide particles having a particle size of 0.001 to 1 μm, or as a metal oxide layer and/or phosphor oxide layer on the surface of the positive electrode active material particles. It is preferable to cover a part of it. Alternatively, the first element may be dissolved in the surface layer of the positive electrode active material particles. Examples of metal oxides include MgO, _Al2O3 , SnO, _ZrO2 , _TiO2 , _BaO , _{B2O3 ,} and the like. Examples of phosphorous oxides include _AlPO4 , _Mg3 ( _PO4 ) ₂ , _Sn3 ( _PO4 ) ₂ , and the like. Moreover, when C is used as the first element, it is preferable that carbon particles having an average particle size of 1 μm or less adhere to the surface of the active material. The amount of the first element metal oxide, phosphorous oxide, and carbon particles is preferably 0.001 to 3% by weight of the positive electrode active material.

The positive electrode active material particles may be in the form of primary particles or secondary particles in which primary particles are agglomerated. Further, primary particles and secondary particles may be mixed.

The average primary particle size of the positive electrode active material particles can be 0.05 μm or more and 3 μm or less. Moreover, the average secondary particle size of the positive electrode active material particles can be set to 3 μm or more and 20 μm or less.

A conductive agent can increase electronic conductivity and suppress contact resistance with a current collector. Examples of conductive agents include acetylene black, carbon black, carbon nanotubes, carbon fibers, and graphite.

The binder can bind the active material and the conductive agent. Examples of binders include polymers such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, carboxymethylcellulose (CMC), and acrylic materials. The binder can impart flexibility to the active material-containing layer containing polymer fibers. PVdF and styrene-butadiene rubber are excellent in increasing flexibility.

The compounding ratio of the positive electrode active material, the conductive agent, and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 19% by weight of the conductive agent, and 1 to 7% by weight of the binder.

The positive electrode is prepared, for example, by suspending a positive electrode active material, a conductive agent and a binder in a suitable solvent, applying the suspension to a current collector made of aluminum foil or an aluminum alloy foil, drying and pressing. produced. The BET specific surface area of the positive electrode active material-containing layer is preferably in the range of 0.1 to 2 m ² /g.

The current collector is preferably aluminum foil or aluminum alloy foil. The thickness of the current collector can be 20 μm or less, more preferably 15 μm or less.

(Non-aqueous electrolyte)
The nonaqueous electrolyte may be a liquid organic electrolyte prepared by dissolving an electrolyte in an organic solvent, a gel organic electrolyte obtained by combining a liquid organic solvent and a polymer material, or a lithium salt electrolyte and a polymer material. Composite solid non-aqueous electrolytes can be mentioned. Further, a room-temperature molten salt (ionic melt) containing lithium ions may be used as the non-aqueous electrolyte. Polymer materials include, for example, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

A liquid organic electrolyte is prepared by dissolving the electrolyte in an organic solvent at a concentration of 0.5 to 2.5 mol/L.

A lithium salt or a sodium salt can be used as the electrolyte. For example, _LiBF4 , _LiPF6 , _LiAsF6 , LiClO4 _{, LiCF3SO3} , LiN _{( CF3SO2 ) 2} , LiN( _{C2F5SO2 ) 2 ,} Li( _{CF3SO2 ) 3C} , LiB [(OCO) ₂ ] ₂ and the like. One type or two or more types of electrolytes can be used. Among them, lithium tetrafluoroborate (LiBF ₄ ) and lithium hexafluorophosphate (LiPF ₆ ) are preferably included. As a result, the chemical stability of the organic solvent is increased, the film resistance on the negative electrode can be reduced, and the low temperature performance and cycle life performance can be significantly improved.

Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC), dimethoxyethane ( DME) and diethoxyethane (DEE), cyclic ethers such as tetrahydrofuran (THF) and dioxolane (DOX), γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). can. These organic solvents can be used alone or in the form of a mixture of two or more. In particular, when one or more selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), and γ-butyrolactone (GBL) is used as the main component, the boiling point becomes 200°C or higher, and the thermal stability increases, which is preferable. . In particular, the inclusion of γ-butyrolactone (GBL) is preferable because the output performance in a low-temperature environment is enhanced. In addition, since it is possible to dissolve and use a lithium salt at a high concentration, it is preferable to dissolve the lithium salt in the organic solvent in a range of 1.5 to 2.5 mol/L. This is because a high output can be obtained even in a low-temperature environment. By setting the lithium salt concentration to 1.5 mol/L or more, it is possible to avoid a rapid decrease in the lithium ion concentration at the interface between the positive electrode and the electrolyte during discharge at a large current, thereby suppressing a significant decrease in output. can be done. On the other hand, by setting the lithium salt concentration to 2.5 mol/L or less, the viscosity of the non-aqueous electrolyte can be lowered to increase the moving speed of lithium ions, and high output can be obtained.

Further, the ambient temperature molten salt (ionic melt) is preferably composed of lithium ions or sodium ions, organic cations and organic anions. Further, the ambient temperature molten salt is desirably liquid at room temperature or below.

An electrolyte containing a room-temperature molten salt will be described below.

Room-temperature molten salt refers to a salt that is at least partially liquid at room temperature, and room temperature refers to the temperature range in which a power supply normally operates. The temperature range in which the power supply is expected to operate normally has an upper limit of about 120°C, possibly about 60°C, and a lower limit of about -40°C, sometimes about -20°C. Among them, a range of -20°C or higher and 60°C or lower is suitable.

As the room-temperature molten salt containing lithium ions, it is desirable to use an ionic melt composed of lithium ions, organic cations and anions. Moreover, the ionic melt is preferably liquid even at room temperature or below.

Examples of organic cations include alkylimidazolium ions and quaternary ammonium ions having a skeleton shown in Chemical Formula 1 below.

Preferred alkylimidazolium ions include dialkylimidazolium ions, trialkylimidazolium ions, and tetraalkylimidazolium ions. As the dialkylimidazolium, 1-methyl-3-ethylimidazolium ion (MEI ⁺ ) is preferred. A preferred trialkylimidazolium ion is 1,2-diethyl-3-propylimidazolium ion (DMPI ⁺ ). As the tetraalkylimidazolium ion, 1,2-diethyl-3,4(5)-dimethylimidazolium ion is preferred.

Preferred quaternary ammonium ions include tetraalkylammonium ions and cyclic ammonium ions. Preferred tetraalkylammonium ions are dimethylethylmethoxyethylammonium ion, dimethylethylmethoxymethylammonium ion, dimethylethylethoxyethylammonium ion and trimethylpropylammonium ion.

By using alkylimidazolium ions or quaternary ammonium ions (especially tetraalkylammonium ions), the melting point can be made 100° C. or lower, more preferably 20° C. or lower. Furthermore, the reactivity with the negative electrode can be lowered.

The concentration of lithium ions is preferably 20 mol % or less. A more preferred range is from 1 to 10 mol %. By setting the temperature within the above range, a liquid room-temperature molten salt can be easily formed even at a low temperature of 20°C or less. In addition, the viscosity can be lowered even below room temperature, and the ionic conductivity can be increased.

Anions include BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , CF ₃ COO ⁻ , CH ₃ COO ⁻ , CO ₃ ² − , (FSO ₂ ) ₂ N ⁻ , N It is preferable to coexist with one or more anions selected from (CF ₃ SO ₂ ) ₂ ⁻ , N(C ₂ F ₅ SO ₂ ) ₂ ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ and the like. A room-temperature molten salt having a melting point of 20° C. or lower can be easily formed by allowing a plurality of anions to coexist. More preferred anions include BF ₄ ⁻ , (FSO ₂ )2N ⁻ , CF ₃ SO ₃ ⁻ , CF ₃ COO ⁻ , CH ₃ COO ⁻ , CO ₃ ²⁻ , N(CF ₃ SO ₂ ) ₂ ⁻ , N( _{C2F5SO2 ) 2-} ^, _{( CF3SO2 ) 3C-} ^. These anions make it easier to form a room temperature molten salt below 0°C.
(separator)
A separator can be placed between the positive electrode and the negative electrode. As a separator, an olefin-based porous film such as polyethylene (PE) or polypropylene (PP), or a separator made of cellulose fiber can be used. The porosity of the separator can be 50% or more. Furthermore, a separator whose surface is coated with inorganic powder can be used.

The fiber diameter of the cellulose fibers is desirably 10 μm or less. Examples of the form of the cellulose fiber separator include nonwoven fabric, film, and paper. In particular, a separator made of cellulose fibers having a porosity of 60% or more has good non-aqueous electrolyte impregnation, and high output performance can be obtained from low to high temperatures. A more preferred range of porosity is 62% to 80%. In addition, by combining the cellulose fiber separator with a porosity of 60% or more with the negative electrode containing the active material according to the first embodiment, the reaction between the separator and the negative electrode during long-term charge storage, float charge, and overcharge is suppressed. It is possible to avoid the problem of short circuit between the negative electrode and the positive electrode due to dendrite deposition of lithium metal. Furthermore, by setting the fiber diameter of the cellulose fiber to 10 μm or less, the affinity between the separator and the non-aqueous electrolyte is improved, and the battery resistance can be reduced. More preferably, it is 3 μm or less.

The separator preferably has a thickness of 10-100 μm, preferably 20-100 μm, and a density of 0.2-0.9 g/cm ³ . Within this range, a balance can be achieved between the mechanical strength and the reduction in battery resistance, and a battery with high output and resistance to internal short-circuiting can be provided. In addition, there is little heat shrinkage in a high-temperature environment, and good high-temperature storage performance can be obtained.

(container)
A metal container or a laminated film container can be used as a container for accommodating the positive electrode, the negative electrode and the non-aqueous electrolyte.

As the metal container, a metal can made of aluminum, an aluminum alloy, iron, stainless steel, or the like and having a rectangular or cylindrical shape can be used. The plate thickness of the container is preferably 0.5 mm or less, more preferably 0.3 mm or less.

Examples of laminate films include multilayer films in which aluminum foil is coated with a resin film. Polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used as the resin. Also, the thickness of the laminate film is preferably 0.2 mm or less. The purity of the aluminum foil is preferably 99.5% or more.

The metal can made of an aluminum alloy is preferably made of an alloy with an aluminum purity of 99.8% or less containing elements such as manganese, magnesium, zinc and silicon. The dramatic increase in the strength of the metal can made of aluminum alloy allows the thickness of the can to be reduced. As a result, it is possible to realize a battery that is thin, lightweight, high in output, and excellent in heat dissipation.

Also, a thin large-sized cup molded body processed using a stainless steel foil (thickness 0.1 to 0.3 mm) not covered with a resin film can be used as a container.

In addition, the type of battery is not limited to a rectangular type, and various types such as a cylindrical type, a thin type, and a coin type can be used. Also, the secondary battery may include an electrode group in which a separator is interposed between a positive electrode and a negative electrode. The shape of the electrode group is not limited to a flat shape, and may be, for example, a cylindrical shape, a laminated shape, or the like.

The secondary battery may further include a positive terminal electrically connected to the positive electrode of the electrode group and a negative terminal electrically connected to the negative electrode of the electrode group.

(negative terminal)
The negative electrode terminal can be made of a material that is electrochemically stable at the Li absorption/discharge potential of the negative electrode active material and has conductivity. Specifically, the material of the negative electrode terminal includes copper, nickel, stainless steel, aluminum, or at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. An aluminum alloy is mentioned. As a material for the negative terminal, it is preferable to use aluminum or an aluminum alloy. In order to reduce contact resistance with the negative electrode current collector, the negative electrode terminal is preferably made of the same material as the negative electrode current collector.

(Positive terminal)
The positive electrode terminal can be made of a material that is electrically stable and conductive in a potential range of 3 V to 4.5 V (vs. Li/Li ⁺ ) relative to the oxidation-reduction potential of lithium. Materials for the positive electrode terminal include aluminum or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu and Si. In order to reduce contact resistance with the positive electrode current collector, the positive electrode terminal is preferably made of the same material as the positive electrode current collector.

A secondary battery of an embodiment may be a secondary battery having a bipolar structure. As a result, there is an advantage that a secondary battery having a voltage equivalent to that of a plurality of series-connected cells can be produced with a single cell.

An example of the secondary battery of the embodiment will be described with reference to FIGS. 1 to 5. FIG.

1 and 2 show an example of a secondary battery using a metal container.

The electrode group 1 is housed in a rectangular tubular metal container 2 . The electrode group 1 has a structure in which a positive electrode active material-containing layer of a positive electrode 3 and a negative electrode active material-containing layer of a negative electrode 4 are spirally wound with a separator 5 interposed between them to form a flat shape. The separator 5 covers the surface of the positive electrode active material containing layer or the negative electrode active material containing layer. As shown in FIG. 2 , strip-shaped positive electrode leads 6 are electrically connected to a plurality of positions on the end of the positive electrode 3 positioned on the end surface of the electrode group 1 . A strip-shaped negative electrode lead 7 is electrically connected to each of a plurality of locations on the end portion of the negative electrode 4 located on this end face. The plurality of positive electrode leads 6 are bundled together and electrically connected to the positive electrode conductive tab 8 . A positive terminal is composed of the positive lead 6 and the positive conductive tab 8 . Further, the negative electrode lead 7 is connected to the negative electrode conductive tab 9 in a bundled state. A negative terminal is composed of the negative lead 7 and the negative conductive tab 9 . The metal sealing plate 10 is fixed to the opening of the metal container 2 by welding or the like. The positive electrode conductive tab 8 and the negative electrode conductive tab 9 are drawn out from holes provided in the sealing plate 10, respectively. The inner peripheral surface of each extraction hole of the sealing plate 10 is covered with an insulating member 11 in order to avoid a short circuit due to contact with the positive electrode conductive tab 8 and the negative electrode conductive tab 9 .

3 and 4 show an example of a secondary battery using a laminated film exterior member.

As shown in FIGS. 3 and 4, the flat wound electrode group 1 is housed in a bag-shaped exterior member 12 made of a laminated film with a metal layer interposed between two resin films. The flat wound electrode group 1 is formed by spirally winding a laminate in which the negative electrode 4, the separator 15, the positive electrode 3, and the separator 15 are laminated in this order from the outside, and press-molding the laminate. As shown in FIG. 4, the outermost negative electrode 4 has a structure in which a negative electrode active material containing layer 4b containing a negative electrode active material is formed on one side of the inner surface of a negative electrode current collector 4a, and the other negative electrodes 4 are negative electrodes. The negative electrode active material containing layer 4b is formed on both surfaces of the current collector 4a. The positive electrode 3 is configured by forming positive electrode active material-containing layers 3b on both sides of a positive electrode current collector 3a.

In the vicinity of the outer peripheral end of the wound electrode group 1, the negative electrode terminal 13 is connected to the negative electrode current collector 4a of the outermost negative electrode 4, and the positive electrode terminal 14 is connected to the positive electrode current collector 3a of the inner positive electrode 3. These negative terminal 13 and positive terminal 14 are extended outside from the opening of the bag-shaped exterior member 12 . The wound electrode group 1 is sealed by heat-sealing the opening of the bag-shaped exterior member 12 . At the time of heat sealing, the negative electrode terminal 13 and the positive electrode terminal 14 are sandwiched by the bag-like exterior member 12 at this opening.

According to the secondary battery of the third embodiment described above, since it includes the active material of the first embodiment or the electrode of the second embodiment, it has a high capacity and is excellent in large current performance and cycle life performance. A secondary battery can be provided.
(Fourth embodiment)
The assembled battery of the fourth embodiment includes a plurality of secondary batteries of the third embodiment.

Examples of the assembled battery include those including a plurality of unit cells electrically connected in series and/or in parallel as a structural unit, a first unit composed of a plurality of electrically series-connected unit cells, or an electrically Examples include those including a second unit composed of a plurality of unit cells connected in parallel. The assembled battery may include at least one form of these configurations.

Examples of forms in which a plurality of secondary batteries are electrically connected in series and/or in parallel include those in which a plurality of batteries each provided with an exterior member are electrically connected in series and/or in parallel; electrical series and/or parallel connection of a plurality of electrode groups or bipolar electrode bodies housed in the . A specific example of the former is to connect positive terminals and negative terminals of a plurality of secondary batteries with a metal bus bar (for example, aluminum, nickel, or copper). In the latter specific example, a plurality of electrode groups or bipolar electrode bodies are housed in one housing while being electrochemically insulated by partition walls, and these are electrically connected in series. In the case of secondary batteries, voltage compatibility with lead-acid batteries can be improved by setting the number of batteries electrically connected in series within the range of 5 to 7. A configuration in which five or six unit cells are connected in series is preferable for higher voltage compatibility with lead-acid batteries.

As a housing for housing the assembled battery, a metal can made of aluminum alloy, iron, stainless steel, or the like, a plastic container, or the like can be used. Moreover, it is desirable that the plate thickness of the container is 0.5 mm or more.

An example of an assembled battery will be described with reference to FIG. The assembled battery 200 shown in FIG. 5 includes a plurality of square secondary batteries 100 ₁ to 100 ₅ shown in FIG. 1 as unit cells. The positive conductive tab 8 of the battery _100-1 and the negative conductive tab 9 of the adjacent battery _100-2 are electrically connected by a lead or bus bar 21. FIG. Furthermore, the positive conductive tab 8 of this battery _100-2 and the negative conductive tab 9 of the adjacent battery _100-3 are electrically connected by leads or bus bars 21. FIG. In this way, the batteries 100 ₁ to 100 ₅ are connected in series.

Since the assembled battery of the fourth embodiment described above includes the secondary battery of the third embodiment, it is possible to achieve high capacity, excellent charge/discharge cycle life, and large current performance.
(Fifth embodiment)
The battery pack according to the fifth embodiment can include one or a plurality of secondary batteries (cells) according to the first embodiment. A plurality of secondary batteries can also be electrically connected in series, parallel, or a combination of series and parallel to form an assembled battery. A battery pack according to the fifth embodiment may include a plurality of assembled batteries.

The battery pack according to the fifth embodiment can further include a protection circuit. The protection circuit has a function of controlling charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses a battery pack as a power source (for example, an electronic device, an automobile, etc.) can also be used as a protection circuit for the battery pack.

Also, the battery pack according to the fifth embodiment can further include an external terminal for power supply. The energizing external terminal is for outputting the current from the secondary battery to the outside and for inputting the current to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for power supply. Also, when charging the battery pack, a charging current (including regenerated energy from the power of a vehicle such as an automobile) is supplied to the battery pack through an external terminal for power supply.

Next, an example of a battery pack according to a fifth embodiment will be described with reference to the drawings.

FIG. 6 is an exploded perspective view schematically showing an example of a battery pack according to the fifth embodiment. 7 is a block diagram showing an example of an electric circuit of the battery pack shown in FIG. 6. FIG.

A battery pack 300 shown in FIGS. 6 and 7 includes a container 31, a lid 32, a protective sheet 33, an assembled battery 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown). .

A storage container 31 shown in FIG. 6 is a bottomed rectangular container having a rectangular bottom surface. The storage container 31 is configured to be able to store the protective sheet 33 , the assembled battery 200 , the printed wiring board 34 , and the wiring 35 . Lid 32 has a rectangular shape. The lid 32 accommodates the assembled battery 200 and the like by covering the container 31 . Although not shown, the storage container 31 and the lid 32 are provided with openings, connection terminals, or the like for connection to an external device or the like.

The assembled battery 200 includes a plurality of single cells 100 , a positive lead 22 , a negative lead 23 , and an adhesive tape 24 .

At least one of the plurality of cells 100 is the secondary battery according to the third embodiment. Each of the plurality of cells 100 is electrically connected in series as shown in FIG. The plurality of single cells 100 may be electrically connected in parallel, or may be connected in a combination of series connection and parallel connection. When a plurality of unit cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

The adhesive tape 24 fastens the plurality of unit cells 100 . Instead of the adhesive tape 24, heat-shrinkable tape may be used to fix the plurality of unit cells 100. FIG. In this case, the protection sheets 33 are placed on both sides of the assembled battery 200 , the heat-shrinkable tape is wrapped around, and then the heat-shrinkable tape is heat-shrunk to bind the plurality of unit cells 100 together.

One end of the positive lead 22 is connected to the assembled battery 200 . One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more cells 100 . One end of the negative lead 23 is connected to the assembled battery 200 . One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more cells 100 .

The printed wiring board 34 is installed along one short-side surface of the inner surface of the container 31 . The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wirings 342a and 343a, an external terminal 350 for conducting electricity, and a positive wiring (positive wiring) 348a. and a negative wiring (negative wiring) 348b. One main surface of the printed wiring board 34 faces one side surface of the assembled battery 200 . An insulating plate (not shown) is interposed between the printed wiring board 34 and the assembled battery 200 .

The other end 22 a of the positive lead 22 is electrically connected to the positive connector 342 . The other end 23 a of the negative lead 23 is electrically connected to the negative connector 343 .

The thermistor 345 is fixed to one main surface of the printed wiring board 34 . The thermistor 345 detects the temperature of each cell 100 and transmits the detection signal to the protection circuit 346 .

An external terminal 350 for conducting electricity is fixed to the other main surface of the printed wiring board 34 . External terminal 350 for power supply is electrically connected to a device outside battery pack 300 . The external terminal 350 for energization includes a positive terminal 352 and a negative terminal 353 .

The protection circuit 346 is fixed to the other main surface of the printed wiring board 34 . The protection circuit 346 is connected to the positive terminal 352 via a positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. Also, the protection circuit 346 is electrically connected to the positive connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the plurality of cells 100 via the wiring 35 .

The protective sheets 33 are arranged on both inner side surfaces in the long side direction of the container 31 and on the inner side surface in the short side direction facing the printed wiring board 34 with the assembled battery 200 interposed therebetween. The protective sheet 33 is made of resin or rubber, for example.

The protection circuit 346 controls charging and discharging of the plurality of cells 100 . In addition, based on the detection signal transmitted from the thermistor 345 or the detection signal transmitted from each unit cell 100 or the assembled battery 200, the protection circuit 346 and the external terminal for energizing the external device. 350 (positive terminal 352, negative terminal 353) is cut off.

Examples of the detection signal transmitted from the thermistor 345 include a signal that detects that the temperature of the unit cell 100 is equal to or higher than a predetermined temperature. Examples of detection signals transmitted from the individual cells 100 or the assembled battery 200 include signals that detect overcharge, overdischarge, and overcurrent of the cells 100 . When detecting overcharge or the like for each unit cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each single cell 100 .

As the protection circuit 346, a circuit included in a device (for example, an electronic device, an automobile, etc.) that uses the battery pack 300 as a power source may be used.

The battery pack 300 also has the external terminals 350 for power supply as described above. Therefore, the battery pack 300 can output current from the assembled battery 200 to an external device and input current from the external device to the assembled battery 200 via the external terminal 350 for power supply. In other words, when the battery pack 300 is used as a power source, current from the assembled battery 200 is supplied to the external device through the external terminals 350 for power supply. Also, when charging the battery pack 300 , a charging current from an external device is supplied to the battery pack 300 through the external terminal 350 for power supply. When this battery pack 300 is used as an on-vehicle battery, the regenerated energy of the motive power of the vehicle can be used as the charging current from the external device.

Note that the battery pack 300 may include a plurality of assembled batteries 200 . In this case, the plurality of assembled batteries 200 may be connected in series, may be connected in parallel, or may be connected in a combination of series connection and parallel connection. Also, the printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive-side lead 22 and the negative-side lead 23 may be used as the positive-side terminal and the negative-side terminal, respectively, of the external terminals for electricity supply.

Such battery packs are used in applications that require excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used as, for example, a power supply for electronic equipment, a stationary battery, and a vehicle battery for various vehicles (including railroad vehicle batteries). Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as a vehicle battery.

The battery pack according to the fifth embodiment includes the active material according to the first embodiment, the electrode according to the second embodiment, the secondary battery according to the third embodiment, or the assembly according to the fourth embodiment. Equipped with batteries. Therefore, it is possible to realize a battery pack having a high capacity and excellent large current performance and cycle life performance.

(Sixth embodiment)
According to a sixth embodiment, a vehicle is provided. This vehicle is equipped with the battery pack according to the fifth embodiment.

In the vehicle according to the sixth embodiment, the battery pack recovers, for example, regenerative energy of power of the vehicle. A vehicle may include a mechanism (eg, a regenerator) that converts the vehicle's kinetic energy into regenerative energy.

Examples of vehicles according to the sixth embodiment include two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, assisted bicycles, and railway vehicles.

The mounting position of the battery pack in the vehicle according to the sixth embodiment is not particularly limited. For example, when the battery pack is installed in an automobile, the battery pack can be installed in the engine compartment of the vehicle, behind the vehicle body, or under the seat.

A vehicle according to the sixth embodiment may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, may be electrically connected in parallel, or may be electrically connected by combining series connection and parallel connection. good too. For example, when each battery pack includes an assembled battery, the assembled batteries may be electrically connected in series or may be electrically connected in parallel. may be connected to Alternatively, if each battery pack contains a single battery, the respective batteries may be electrically connected in series, electrically in parallel, or a combination of series and parallel connections. may be electrically connected.

Next, an example of a vehicle according to a sixth embodiment will be described with reference to the drawings.

FIG. 8 is a partially transparent view schematically showing an example of a vehicle according to the sixth embodiment.

A vehicle 400 shown in FIG. 8 includes a vehicle body 40 and a battery pack 300 according to the fifth embodiment. In the example shown in FIG. 8, vehicle 400 is a four-wheeled automobile.

This vehicle 400 may be equipped with a plurality of battery packs 300 . In this case, the batteries (eg, cells or assembled batteries) included in the battery pack 300 may be connected in series, connected in parallel, or connected in a combination of series connection and parallel connection.

FIG. 8 shows an example in which the battery pack 300 is installed in the engine room located in front of the vehicle body 40 . As described above, battery pack 300 may be mounted, for example, in the rear of vehicle body 40 or under the seat. This battery pack 300 can be used as a power source for vehicle 400 . Also, this battery pack 300 can recover the regenerated energy of the power of the vehicle 400 .

Next, an embodiment of the vehicle according to the sixth embodiment will be described with reference to FIG.

FIG. 9 is a diagram schematically showing an example of a control system for an electrical system in a vehicle according to the sixth embodiment. A vehicle 400 shown in FIG. 9 is an electric vehicle.

A vehicle 400 shown in FIG. 9 includes a vehicle main body 40, a vehicle power source 41, a vehicle ECU (ECU: Electric Control Unit) 42 that is a control device higher than the vehicle power source 41, and an external terminal (external A terminal 43 for connecting to a power supply, an inverter 44 and a drive motor 45 are provided.

A vehicle 400 is equipped with a vehicle power source 41, for example, in an engine room, in the rear of a vehicle body, or under a seat. In the vehicle 400 shown in FIG. 9, the locations where the vehicle power supply 41 is mounted are schematically shown.

The vehicle power supply 41 includes a plurality (eg, three) of battery packs 300 a , 300 b and 300 c , a battery management unit (BMU) 411 , and a communication bus 412 .

The battery pack 300a includes an assembled battery 200a and an assembled battery monitoring device 301a (for example, VTM: Voltage Temperature Monitoring). The battery pack 300b includes an assembled battery 200b and an assembled battery monitoring device 301b. The battery pack 300c includes an assembled battery 200c and an assembled battery monitoring device 301c. Battery packs 300a to 300c are battery packs similar to battery pack 300 described above, and assembled batteries 200a to 200c are assembled batteries similar to assembled battery 200 described above. The assembled batteries 200a-200c are electrically connected in series. Battery packs 300 a , 300 b , and 300 c can be independently removed and replaced with another battery pack 300 .

Each of the assembled batteries 200a to 200c includes a plurality of cells connected in series. At least one of the plurality of cells is the secondary battery according to the third embodiment. The assembled batteries 200a to 200c charge and discharge through the positive terminal 413 and the negative terminal 414, respectively.

The battery management device 411 communicates with the assembled battery monitoring devices 301a to 301c, and collects information on the voltage, temperature, etc. of each of the cells 100 included in the assembled batteries 200a to 200c included in the vehicle power supply 41. do. Thereby, the battery management device 411 collects information on maintenance of the vehicle power source 41 .

The battery management device 411 and the assembled battery monitoring devices 301 a to 301 c are connected via a communication bus 412 . In communication bus 412, one set of communication lines is shared by a plurality of nodes (battery management device 411 and one or more assembled battery monitoring devices 301a to 301c). The communication bus 412 is, for example, a communication bus configured based on the CAN (Control Area Network) standard.

The assembled battery monitoring devices 301a to 301c measure the voltage and temperature of the individual single cells forming the assembled batteries 200a to 200c based on commands by communication from the battery management device 411. FIG. However, the temperature can be measured at only a few points per assembled battery, and it is not necessary to measure the temperature of all the single cells.

The vehicle power source 41 can also have an electromagnetic contactor (for example, the switch device 415 shown in FIG. 9) that switches between the presence or absence of electrical connection between the positive terminal 413 and the negative terminal 414 . The switch device 415 includes a precharge switch (not shown) that is turned on when the battery packs 200a to 200c are charged, and a switch device that is turned on when the output from the battery packs 200a to 200c is supplied to the load. and a main switch (not shown). Each of the precharge switch and the main switch has a relay circuit (not shown) that is switched on or off by a signal supplied to a coil arranged near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on control signals from the battery management device 411 or the vehicle ECU 42 that controls the operation of the vehicle 400 as a whole.

The inverter 44 converts the input DC voltage into a three-phase alternating current (AC) high voltage for driving the motor. Three-phase output terminals of the inverter 44 are connected to respective three-phase input terminals of the drive motor 45 . The inverter 44 is controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 for controlling the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

The drive motor 45 is rotated by power supplied from the inverter 44 . A driving force generated by the rotation of the driving motor 45 is transmitted to the axle and the driving wheels W via, for example, a differential gear unit.

In addition, although not shown, vehicle 400 includes a regenerative braking mechanism. The regenerative braking mechanism rotates the drive motor 45 when the vehicle 400 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative brake mechanism is input to the inverter 44 and converted into direct current. The converted DC current is input to vehicle power source 41 .

One terminal of the connection line L<b>1 is connected to the negative terminal 414 of the vehicle power source 41 . The other terminal of the connection line L1 is connected to the negative input terminal 417 of the inverter 44 . A current detection unit (current detection circuit) 416 in the battery management device 411 is provided between the negative terminal 414 and the negative input terminal 417 on the connection line L1.

One terminal of the connection line L2 is connected to the positive terminal 413 of the vehicle power source 41 . The other terminal of the connection line L2 is connected to the positive input terminal 418 of the inverter 44 . A switch device 415 is provided between the positive terminal 413 and the positive input terminal 418 on the connection line L2.

The external terminal 43 is connected to the battery management device 411 . The external terminal 43 can be connected to, for example, an external power supply.

The vehicle ECU 42 cooperatively controls the vehicle power source 41, the switch device 415, the inverter 44, and the like together with other management devices and control devices including the battery management device 411 in response to operation input by the driver or the like. The cooperative control of the vehicle ECU 42 and the like controls the output of electric power from the vehicle power source 41, the charging of the vehicle power source 41, and the like, and manages the vehicle 400 as a whole. Between the battery management device 411 and the vehicle ECU 42, data transfer related to the maintenance of the vehicle power source 41, such as the remaining capacity of the vehicle power source 41, is performed via a communication line.

A vehicle according to the sixth embodiment is equipped with the battery pack according to the fifth embodiment. Therefore, it is possible to realize a vehicle with excellent running performance over a wide temperature range from low to high temperatures.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the embodiments listed below.
(Example 1)
Lithium nickel cobalt manganese oxide (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ) having an average secondary particle size of 5 μm was used as the positive electrode active material. 5% by weight of acetylene black as a conductive agent and 5% by weight of PVdF as a binder were mixed with 90% by weight of the positive electrode active material. After dispersing these in an n-methylpyrrolidone (NMP) solvent to prepare a slurry, the slurry was applied to both sides of a 15 μm thick aluminum alloy foil (purity 99%), dried, and subjected to a pressing process. A positive electrode having a thickness of the positive electrode material layer (positive electrode active material-containing layer) of 38 μm and an electrode density of 2.0 g/cm ³ was produced.

Next, in order to synthesize a negative electrode active material, titanium oxide powder (anatase-type TiO ₂ ) having an average particle size of 0.1 μm and niobium pentoxide powder having an average particle size of 0.1 μm (Nb ₂ O ₅ : purity 99.9% , containing 0.05% K and 0.05% Ta) were weighed and mixed at a molar ratio of 1:1. This powder was heat-treated at 1000° C. for 20 hours. A diffraction pattern was obtained from powder X-ray diffraction measurement of the obtained sample, and it was confirmed from the results of crystal structure analysis by the Rietveld method that the synthesized sample had the desired monoclinic crystals. The average primary particle size was 1 μm.

The molar ratio of Ti and Nb elements was obtained by performing ICP analysis. Specifically, in the ICP analysis, an active material to be a sample was once weighed in a Pt crucible and decomposed by alkali fusion to prepare a measurement solution. Then, Nb and Ti were quantitatively measured by ICP emission spectrometry using an internal standard method (SPS-4000 manufactured by Hitachi High-Tech Science Co., Ltd.). _As a result, the composition of _the sample was expressed _{as TiK0.002Ta0.001Nb1.99O7} . The ratio of Nb mole number to Ti mole number (α/β) was 1.99.
The resulting TiK _0.002 Ta _0.001 Nb _1.99 O ₇ powder was dispersed with 5% by weight of multi-walled carbon nanotube (MCNT) powder containing metal elements consisting of Co, Ni and Fe with an average fiber diameter of 20 nm. It was added to the aqueous solution and stirred to mix and uniformly dispersed. The ratio (γ/σ) of the metal element weight to the carbon weight of the carbon fiber was 0.001 as measured by the method described above. Also, the ratio of the fiber length to the fiber diameter of the carbon fibers (fiber length/fiber diameter) was 200. After that, cellulose nanofiber (CeNF), carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binders, and graphite and acetylene black (AB) as conductive agents are added to this dispersion, and rotated using a ball mill. Stirring was performed at several 1000 rpm for a stirring time of 2 hours to prepare a negative electrode slurry. _The weight ratio of _{TiK0.002Ta0.001Nb1.99O7} , MCNT, graphite, AB, CeNF, _CMC and _SBR was adjusted to 90:2:3:1:1:1:2. Table 1 below shows the carbon fiber addition ratio (the ratio of the carbon fiber weight to the weight of the niobium-titanium composite oxide particles).
The resulting slurry was applied to a 15 μm-thick aluminum foil (purity 99.3%), dried, and subjected to a hot press process to reduce the thickness of the negative electrode material layer (negative electrode active material-containing layer) per side. A negative electrode having a thickness of 30 μm and an electrode density of 2.7 g/cm ³ was produced. The BET specific surface area (surface area per 1 g of the negative electrode material layer) of the negative electrode material layer was 5 m ² /g.

On the other hand, a regenerated cellulose fiber separator made from pulp and having a thickness of 12 μm, a porosity of 65%, and an average fiber diameter of 1 μm was brought into contact with and covered with the positive electrode. The negative electrode was stacked so as to face the positive electrode with the separator interposed therebetween, and the negative electrode active material-containing layer was covered with the negative electrode active material-containing layer with the separator interposed therebetween.

This electrode group was further pressed to form a flat shape. The electrode group was housed in a container made of a thin metal can made of an aluminum alloy (Al purity 99%) having a thickness of 0.3 mm.

On the other hand, as an organic solvent, lithium hexafluorophosphate (LiPF ₆ ) as a lithium salt was added to a mixed solvent of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (volume ratio 25:25:50). was dissolved at 1.2 mol/L to prepare a liquid organic electrolyte (non-aqueous electrolyte). This non-aqueous electrolyte was injected into the electrode group in the container to fabricate a thin non-aqueous electrolyte secondary battery having the structure shown in FIG. The battery had a discharge capacity of 10 Ah and an intermediate voltage (voltage at 50% discharge) of 2.25V.
(Examples 2-18 and Comparative Examples 1-6)
molar ratio (α/β), type of metal element in carbon fiber, weight ratio (γ/σ), average fiber diameter of carbon fiber, type and w of element M, average primary particle size of niobium titanium composite oxide particles, A thin non-aqueous electrolyte secondary battery was fabricated in the same manner as described in Example 1, except that the addition ratio of carbon fiber (carbon fiber/niobium titanium composite oxide) was as shown in Tables 1 and 2 below. bottom.

The obtained secondary battery was charged at a constant current of 1 C rate at 25° C. to 3.0 V in 1.5 hours, and then discharged to 1.5 V at a 1 C rate to measure the discharge capacity. As a cycle test, after charging to 3.0 V in 1.5 hours at a constant current of 1 C rate at 25 ° C., charging and discharging cycles of discharging to 1.5 V at a 1 C rate were repeated, and the capacity decrease width was 20%. The number of cycles was taken as the number of cycle life. As the large current discharge performance, the capacity retention ratio of the 10C discharge capacity to the 1C discharge capacity was determined. These measurement results are shown in Tables 3 and 4 below.

As is clear from Tables 1 to 4, the batteries of Examples 1 to 18 achieved battery capacities equal to or greater than those of Comparative Examples 1 to 6 , while maintaining cycle life and large current discharge performance (10C discharge capacity retention rate ) is superior to Comparative Examples 1-6 . In particular, Examples 2, 3, 6, 10 and 16 were excellent in battery capacity. In terms of large current discharge performance, Examples 3, 9 and 16 obtained excellent performance. Moreover, in terms of cycle life, Examples 1, 3, 5, 7, 9, 11, 16 and 17 obtained excellent performance.

Further, by comparing Examples 3 and 13 to 17, in the range of 0.1% by weight or more and 5% by weight or less, the higher the addition ratio, the better the discharge capacity, the cycle life, and the large current discharge performance. It can be seen that

Comparing Examples 11 and 12 with other examples in which the average fiber diameter of the carbon fibers is in the range of 10 nm or more and 90 nm or less, Examples 11 and 12 are excellent in cycle life performance and are at a high level. On the other hand, the large current discharge performance remains in the 70% range. From the results of Examples 6, 7, 8, and 18, it can be said that the smaller the average primary particle size is, the better the large current discharge performance is, and the larger the average primary particle size is, the better the cycle life performance is likely to be obtained.

Comparative Example 1 satisfies the formula (1) and contains monoclinic niobium-titanium composite oxide particles having an average primary particle size of 0.05 μm or more and 2 μm or less. Life and large current discharge performance are inferior to those of Examples. Comparative Example 2 has a lower capacity than Comparative Example 1 because not only does it contain no carbon fiber, but also the composition of the niobium-titanium composite oxide particles is outside the formula (1). Comparative Examples 3 to 5 satisfy the formula (1), but the formula (2), w and the average primary particle size are out of the appropriate range, so the capacity, cycle life and high current discharge performance are lower than those of the examples. inferior. On the other hand, in Comparative Example 6, the formulas (1) and (2), w, and the average primary particle size were out of the appropriate ranges, so the capacity, cycle life, and high-current discharge performance were inferior to those of Examples. there is

SEM photographs of the negative electrode active material of Example 1 are shown in FIGS. As shown in FIG. 10, the niobium-titanium composite oxide particles 500 within the field of view contain few aggregated particles and many independent primary particles. The SEM photograph shown in FIG. 11 is an enlarged view of the niobium-titanium composite oxide particles 500 . As shown in FIG. 11 , carbon nanotubes 501 adhere to at least part of the surface of niobium-titanium composite oxide particles 500 . As for the negative electrode active materials of Examples 2 to 18, it was confirmed by SEM observation that carbon nanotubes adhered to at least part of the surface of the niobium-titanium composite oxide particles.

According to the active material of at least one embodiment or example described above, the monoclinic niobium-titanium composite oxide particles satisfying the formula (1) and having an average primary particle size of 0.05 μm or more and 2 μm or less, and Fe , contains one or more metal elements selected from the group consisting of Co and Ni, satisfies the formula (2), and has an average fiber diameter of 5 nm or more and 100 nm or less. and cycle life performance can be provided.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1... Electrode group 2... Container (packing member) 3... Positive electrode 3a... Positive electrode collector 3b... Positive electrode active material containing layer 4... Negative electrode 4a... Negative electrode collector 4b... Negative electrode active material containing layer , 5... separator, 6... positive electrode lead, 7... negative electrode lead, 8... positive electrode conductive tab, 9... negative electrode conductive tab, 10... sealing plate, 11... insulating member, 12... exterior member, 13... negative electrode terminal, 14... positive electrode Terminal 21 Lead (bus bar) 34 Printed wiring board 40 Vehicle body 41 Vehicle power supply 42 Vehicle ECU 43 External terminal 44 Inverter 45 Drive motor 100 Unit battery 100 ₁ to 100 ₅ secondary battery 200 assembled battery 200a to c assembled battery 300 battery pack 300a to c battery pack 301a to c assembled battery monitoring device 345 thermistor 346 protection Circuit 350 External terminals for energization 400 Vehicle 411 Battery management device 412 Communication bus 413 Positive terminal 414 Negative terminal L1, L2 Connection line W Drive wheel.

Claims (12)

Monoclinic niobium-titanium composite oxide particles that satisfy the following formula (1) and are capable of intercalating and deintercalating Li ions;
An average fiber diameter of 5 nm, which covers at least part of the surface of the niobium-titanium composite oxide particles, contains one or more metal elements selected from the group consisting of Fe, Co and Ni, and satisfies the following formula (2): and carbon fibers having a diameter of 100 nm or less, and the niobium-titanium composite oxide particles have an average primary particle diameter of 0.05 μm or more and 2 μm or less.
1.5≦(α/β)≦2.5 (1)
1/10000≤(γ/σ)≤1/100 (2)
where α is the number of moles of Nb in the niobium-titanium composite oxide particles, β is the number of moles of Ti in the niobium-titanium composite oxide particles, γ is the weight of all metal elements in the carbon fiber, and σ is the carbon is the carbon weight of the fiber.
The niobium-titanium composite oxide particles are Li _x TiM _w Nb _2±y O _7±z (0≦x≦5, 0≦y≦0.5, −0.3≦z≦0.3, 0≦w≦ 0.01, and M is at least one kind of metal other than Ti and Nb). 3. The active material according to claim 2, wherein said M includes at least one metal element selected from the group consisting of K and Ta. 4. The active material according to claim 2, wherein w satisfies the following formula (3).
0.001≤w≤0.005 (3) The active material according to any one of claims 1 to 4, wherein the value of (γ/σ) satisfies the following formula (4).
1.5/10000≤(γ/σ)≤1/1000 (4) An electrode comprising the active material according to any one of claims 1-5. A secondary battery comprising a positive electrode, a negative electrode containing the active material according to any one of claims 1 to 5, and a non-aqueous electrolyte. A battery pack comprising the secondary battery according to claim 7 . an external terminal for energization;
9. The battery pack of claim 8, further comprising a protection circuit. comprising a plurality of the secondary batteries,
The battery pack according to claim 8 or 9, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle equipped with the battery pack according to any one of claims 8 to 10. 12. The vehicle of claim 11, including a mechanism for converting kinetic energy of the vehicle into regenerative energy.

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